/**
 * Funf: Open Sensing Framework
 * Copyright (C) 2010-2011 Nadav Aharony, Wei Pan, Alex Pentland. 
 * Acknowledgments: Alan Gardner
 * Contact: nadav@media.mit.edu
 * 
 * This file is part of Funf.
 * 
 * Funf is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as 
 * published by the Free Software Foundation, either version 3 of 
 * the License, or (at your option) any later version. 
 * 
 * Funf is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of 
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
 * See the GNU Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public 
 * License along with Funf. If not, see <http://www.gnu.org/licenses/>.
 */
package edu.mit.media.funf.probe.builtin;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import android.os.Bundle;
import android.util.Log;
import edu.mit.media.funf.Utils;
import edu.mit.media.funf.probe.Probe;
import edu.mit.media.funf.probe.builtin.ProbeKeys.TimeOffsetKeys;

/**
 * Broadcasts the current system time offset from time on major NTP servers in seconds.
 * Uses "2.north-america.pool.ntp.org"
 *
 */
public class TimeOffsetProbe extends Probe implements TimeOffsetKeys {
	
	private Thread runningThread;
	private Double mostRecentTimeOffset;
	
	@Override
	public Parameter[] getAvailableParameters() {
		return new Parameter[] {
			new Parameter(Parameter.Builtin.PERIOD, 86400L),
			new Parameter(Parameter.Builtin.START, 0L),
			new Parameter(Parameter.Builtin.END, 0L),
		};
	}

	@Override
	public String[] getRequiredFeatures() {
		return null;
	}

	@Override
	public String[] getRequiredPermissions() {
		return new String[] {
			android.Manifest.permission.INTERNET
		};
	}

	@Override
	protected void onEnable() {
		mostRecentTimeOffset = null;
		runningThread = null;
	}
	
	@Override
	protected void onDisable() {
		// Nothing
	}

	@Override
	protected void onRun(Bundle params) {
		if (runningThread == null) {
			runningThread = new Thread(new Runnable() {
				@Override
				public void run() {
					try {
						mostRecentTimeOffset = truncate(SntpClient.returnSystemTimeOffsetMilliSeconds());
						sendProbeData();
					} catch (IOException e) {
						Log.w(TAG, "Unable to access time servers");
					} finally {
						runningThread = null;
						stop();
					}
				}
			});
			runningThread.start();
		}
	}
	
	private static double truncate(double number) {
		return ((double)((long)(number * 1000)))/1000.0d;
	}

	@Override
	protected void onStop() {
		if (runningThread != null && runningThread.isAlive()) {
			runningThread = null;
		}
	}

	@Override
	public void sendProbeData() {
		if (mostRecentTimeOffset != null) {
			Bundle data = new Bundle();
			data.putDouble(TIME_OFFSET, mostRecentTimeOffset);
			sendProbeData(Utils.getTimestamp(), data);
		}
	}

	
	/**
	 * NtpClient - an NTP client for Java.  This program connects to an NTP server
	 * and prints the response to the console.
	 * 
	 * The local clock offset calculation is implemented according to the SNTP
	 * algorithm specified in RFC 2030.  
	 * 
	 * Note that on windows platforms, the curent time-of-day timestamp is limited
	 * to an resolution of 10ms and adversely affects the accuracy of the results.
	 * 
	 * 
	 * This code is copyright (c) Adam Buckley 2004
	 *
	 * This program is free software; you can redistribute it and/or modify it 
	 * under the terms of the GNU General Public License as published by the Free 
	 * Software Foundation; either version 2 of the License, or (at your option) 
	 * any later version.  A HTML version of the GNU General Public License can be
	 * seen at http://www.gnu.org/licenses/gpl.html
	 *
	 * This program is distributed in the hope that it will be useful, but WITHOUT 
	 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
	 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for 
	 * more details.
	 *  
	 * @author Adam Buckley
	 */
	public static class SntpClient
	{
		
		public static final String TAG = "NTP TIME SYNC";
		public static double returnSystemTimeOffsetMilliSeconds() throws IOException {
			String serverName = "2.north-america.pool.ntp.org";
			
			// Send request
			DatagramSocket socket = new DatagramSocket();
			InetAddress address = InetAddress.getByName(serverName);
			byte[] buf = new NtpMessage().toByteArray();
			DatagramPacket packet =
				new DatagramPacket(buf, buf.length, address, 123);
			
			// Set the transmit timestamp *just* before sending the packet
			// ToDo: Does this actually improve performance or not?
			NtpMessage.encodeTimestamp(packet.getData(), 40,
				(System.currentTimeMillis()/1000.0) + 2208988800.0);
			socket.setSoTimeout(8000);
			socket.send(packet);
			
			
			// Get response
			Log.i(TAG, "NTP request sent, waiting for response...\n");
			packet = new DatagramPacket(buf, buf.length);
			socket.receive(packet);
			
			// Immediately record the incoming timestamp
			double destinationTimestamp =
				(System.currentTimeMillis()/1000.0) + 2208988800.0;
			
			
			// Process response
			NtpMessage msg = new NtpMessage(packet.getData());
			
			// Corrected, according to RFC2030 errata
			double roundTripDelay = (destinationTimestamp-msg.originateTimestamp) -
				(msg.transmitTimestamp-msg.receiveTimestamp);
				
			double localClockOffset =
				((msg.receiveTimestamp - msg.originateTimestamp) +
				(msg.transmitTimestamp - destinationTimestamp)) / 2;
			
			
			// Display response
			/*
			System.out.println("NTP server: " + serverName);
			System.out.println(msg.toString());
			
			System.out.println("Dest. timestamp:     " +
				NtpMessage.timestampToString(destinationTimestamp));
			
			System.out.println("Round-trip delay: " +
				new DecimalFormat("0.00").format(roundTripDelay*1000) + " ms");
			
			System.out.println("Local clock offset: " +
				new DecimalFormat("0.00").format(localClockOffset*1000) + " ms");
			*/
			// cannot change the system clock due to time difference
			// SystemClock.setCurrentTimeMillis(System.currentTimeMillis() + (long)(localClockOffset*1000));
			socket.close();
			return localClockOffset;
		}
	}
		
		
		/**
		 * This class represents a NTP message, as specified in RFC 2030.  The message
		 * format is compatible with all versions of NTP and SNTP.
		 *
		 * This class does not support the optional authentication protocol, and
		 * ignores the key ID and message digest fields.
		 * 
		 * For convenience, this class exposes message values as native Java types, not
		 * the NTP-specified data formats.  For example, timestamps are
		 * stored as doubles (as opposed to the NTP unsigned 64-bit fixed point
		 * format).
		 * 
		 * However, the contructor NtpMessage(byte[]) and the method toByteArray()
		 * allow the import and export of the raw NTP message format.
		 * 
		 * 
		 * Usage example
		 * 
		 * // Send message
		 * DatagramSocket socket = new DatagramSocket();
		 * InetAddress address = InetAddress.getByName("ntp.cais.rnp.br");
		 * byte[] buf = new NtpMessage().toByteArray();
		 * DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 123);
		 * socket.send(packet);
		 * 
		 * // Get response
		 * socket.receive(packet);
		 * System.out.println(msg.toString());
		 * 
		 *  
		 * This code is copyright (c) Adam Buckley 2004
		 *
		 * This program is free software; you can redistribute it and/or modify it 
		 * under the terms of the GNU General Public License as published by the Free 
		 * Software Foundation; either version 2 of the License, or (at your option) 
		 * any later version.  A HTML version of the GNU General Public License can be
		 * seen at http://www.gnu.org/licenses/gpl.html
		 *
		 * This program is distributed in the hope that it will be useful, but WITHOUT 
		 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
		 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for 
		 * more details.
		 * 
		 * 
		 * Comments for member variables are taken from RFC2030 by David Mills,
		 * University of Delaware.
		 * 
		 * Number format conversion code in NtpMessage(byte[] array) and toByteArray()
		 * inspired by http://www.pps.jussieu.fr/~jch/enseignement/reseaux/
		 * NTPMessage.java which is copyright (c) 2003 by Juliusz Chroboczek
		 * 
		 * @author Adam Buckley
		 */
		public static class NtpMessage
		{
			/**
			 * This is a two-bit code warning of an impending leap second to be
			 * inserted/deleted in the last minute of the current day.  It's values
			 * may be as follows:
			 * 
			 * Value     Meaning
			 * -----     -------
			 * 0         no warning
			 * 1         last minute has 61 seconds
			 * 2         last minute has 59 seconds)
			 * 3         alarm condition (clock not synchronized)
			 */
			public byte leapIndicator = 0;
			
			
			/**
			 * This value indicates the NTP/SNTP version number.  The version number
			 * is 3 for Version 3 (IPv4 only) and 4 for Version 4 (IPv4, IPv6 and OSI).
			 * If necessary to distinguish between IPv4, IPv6 and OSI, the
			 * encapsulating context must be inspected.
			 */
			public byte version = 3;
			
			
			/**
			 * This value indicates the mode, with values defined as follows:
			 * 
			 * Mode     Meaning
			 * ----     -------
			 * 0        reserved
			 * 1        symmetric active
			 * 2        symmetric passive
			 * 3        client
			 * 4        server
			 * 5        broadcast
			 * 6        reserved for NTP control message
			 * 7        reserved for private use
			 * 
			 * In unicast and anycast modes, the client sets this field to 3 (client)
			 * in the request and the server sets it to 4 (server) in the reply. In
			 * multicast mode, the server sets this field to 5 (broadcast).
			 */ 
			public byte mode = 0;
			
			
			/**
			 * This value indicates the stratum level of the local clock, with values
			 * defined as follows:
			 * 
			 * Stratum  Meaning
			 * ----------------------------------------------
			 * 0        unspecified or unavailable
			 * 1        primary reference (e.g., radio clock)
			 * 2-15     secondary reference (via NTP or SNTP)
			 * 16-255   reserved
			 */
			public short stratum = 0;
			

			/**
			 * This value indicates the maximum interval between successive messages,
			 * in seconds to the nearest power of two. The values that can appear in
			 * this field presently range from 4 (16 s) to 14 (16284 s); however, most
			 * applications use only the sub-range 6 (64 s) to 10 (1024 s).
			 */
			public byte pollInterval = 0;
			
			
			/**
			 * This value indicates the precision of the local clock, in seconds to
			 * the nearest power of two.  The values that normally appear in this field
			 * range from -6 for mains-frequency clocks to -20 for microsecond clocks
			 * found in some workstations.
			 */
			public byte precision = 0;
			
			
			/**
			 * This value indicates the total roundtrip delay to the primary reference
			 * source, in seconds.  Note that this variable can take on both positive
			 * and negative values, depending on the relative time and frequency
			 * offsets. The values that normally appear in this field range from
			 * negative values of a few milliseconds to positive values of several
			 * hundred milliseconds.
			 */
			public double rootDelay = 0;
			
			
			/**
			 * This value indicates the nominal error relative to the primary reference
			 * source, in seconds.  The values  that normally appear in this field
			 * range from 0 to several hundred milliseconds.
			 */ 
			public double rootDispersion = 0;
			
			
			/**
			 * This is a 4-byte array identifying the particular reference source.
			 * In the case of NTP Version 3 or Version 4 stratum-0 (unspecified) or
			 * stratum-1 (primary) servers, this is a four-character ASCII string, left
			 * justified and zero padded to 32 bits. In NTP Version 3 secondary
			 * servers, this is the 32-bit IPv4 address of the reference source. In NTP
			 * Version 4 secondary servers, this is the low order 32 bits of the latest
			 * transmit timestamp of the reference source. NTP primary (stratum 1)
			 * servers should set this field to a code identifying the external
			 * reference source according to the following list. If the external
			 * reference is one of those listed, the associated code should be used.
			 * Codes for sources not listed can be contrived as appropriate.
			 * 
			 * Code     External Reference Source
			 * ----     -------------------------
			 * LOCL     uncalibrated local clock used as a primary reference for
			 *          a subnet without external means of synchronization
			 * PPS      atomic clock or other pulse-per-second source
			 *          individually calibrated to national standards
			 * ACTS     NIST dialup modem service
			 * USNO     USNO modem service
			 * PTB      PTB (Germany) modem service
			 * TDF      Allouis (France) Radio 164 kHz
			 * DCF      Mainflingen (Germany) Radio 77.5 kHz
			 * MSF      Rugby (UK) Radio 60 kHz
			 * WWV      Ft. Collins (US) Radio 2.5, 5, 10, 15, 20 MHz
			 * WWVB     Boulder (US) Radio 60 kHz
			 * WWVH     Kaui Hawaii (US) Radio 2.5, 5, 10, 15 MHz
			 * CHU      Ottawa (Canada) Radio 3330, 7335, 14670 kHz
			 * LORC     LORAN-C radionavigation system
			 * OMEG     OMEGA radionavigation system
			 * GPS      Global Positioning Service
			 * GOES     Geostationary Orbit Environment Satellite
			 */
			public byte[] referenceIdentifier = {0, 0, 0, 0};
			
			
			/**
			 * This is the time at which the local clock was last set or corrected, in
			 * seconds since 00:00 1-Jan-1900.
			 */
			public double referenceTimestamp = 0;
			
			
			/**
			 * This is the time at which the request departed the client for the
			 * server, in seconds since 00:00 1-Jan-1900.
			 */
			public double originateTimestamp = 0;
			
			
			/**
			 * This is the time at which the request arrived at the server, in seconds
			 * since 00:00 1-Jan-1900.
			 */
			public double receiveTimestamp = 0;
			
			
			/**
			 * This is the time at which the reply departed the server for the client,
			 * in seconds since 00:00 1-Jan-1900.
			 */
			public double transmitTimestamp = 0;
			
			
			
			/**
			 * Constructs a new NtpMessage from an array of bytes.
			 */
			public NtpMessage(byte[] array)
			{
				// See the packet format diagram in RFC 2030 for details 
				leapIndicator = (byte) ((array[0] >> 6) & 0x3);
				version = (byte) ((array[0] >> 3) & 0x7);
				mode = (byte) (array[0] & 0x7);
				stratum = unsignedByteToShort(array[1]);
				pollInterval = array[2];
				precision = array[3];
				
				rootDelay = (array[4] * 256.0) + 
					unsignedByteToShort(array[5]) +
					(unsignedByteToShort(array[6]) / 256.0) +
					(unsignedByteToShort(array[7]) / 65536.0);
				
				rootDispersion = (unsignedByteToShort(array[8]) * 256.0) + 
					unsignedByteToShort(array[9]) +
					(unsignedByteToShort(array[10]) / 256.0) +
					(unsignedByteToShort(array[11]) / 65536.0);
				
				referenceIdentifier[0] = array[12];
				referenceIdentifier[1] = array[13];
				referenceIdentifier[2] = array[14];
				referenceIdentifier[3] = array[15];
				
				referenceTimestamp = decodeTimestamp(array, 16);
				originateTimestamp = decodeTimestamp(array, 24);
				receiveTimestamp = decodeTimestamp(array, 32);
				transmitTimestamp = decodeTimestamp(array, 40);
			}
			
			
			
			/**
			 * Constructs a new NtpMessage in client -> server mode, and sets the
			 * transmit timestamp to the current time.
			 */
			public NtpMessage()
			{
				// Note that all the other member variables are already set with
				// appropriate default values.
				this.mode = 3;
				this.transmitTimestamp = (System.currentTimeMillis()/1000.0) + 2208988800.0; 
			}
			
			
			
			/**
			 * This method constructs the data bytes of a raw NTP packet.
			 */
			public byte[] toByteArray()
			{
				// All bytes are automatically set to 0
				byte[] p = new byte[48];

				p[0] = (byte) (leapIndicator << 6 | version << 3 | mode);
				p[1] = (byte) stratum;
				p[2] = (byte) pollInterval;
				p[3] = (byte) precision;
				
				// root delay is a signed 16.16-bit FP, in Java an int is 32-bits
				int l = (int) (rootDelay * 65536.0);
				p[4] = (byte) ((l >> 24) & 0xFF);
				p[5] = (byte) ((l >> 16) & 0xFF);
				p[6] = (byte) ((l >> 8) & 0xFF);
				p[7] = (byte) (l & 0xFF);
				
				// root dispersion is an unsigned 16.16-bit FP, in Java there are no
				// unsigned primitive types, so we use a long which is 64-bits 
				long ul = (long) (rootDispersion * 65536.0);
				p[8] = (byte) ((ul >> 24) & 0xFF);
				p[9] = (byte) ((ul >> 16) & 0xFF);
				p[10] = (byte) ((ul >> 8) & 0xFF);
				p[11] = (byte) (ul & 0xFF);
				
				p[12] = referenceIdentifier[0];
				p[13] = referenceIdentifier[1];
				p[14] = referenceIdentifier[2];
				p[15] = referenceIdentifier[3];
				
				encodeTimestamp(p, 16, referenceTimestamp);
				encodeTimestamp(p, 24, originateTimestamp);
				encodeTimestamp(p, 32, receiveTimestamp);
				encodeTimestamp(p, 40, transmitTimestamp);
				
				return p; 
			}
			
			
			
			/**
			 * Returns a string representation of a NtpMessage
			 */
			public String toString()
			{
				String precisionStr =
					new DecimalFormat("0.#E0").format(Math.pow(2, precision));
					
				return "Leap indicator: " + leapIndicator + "\n" +
					"Version: " + version + "\n" +
					"Mode: " + mode + "\n" +
					"Stratum: " + stratum + "\n" +
					"Poll: " + pollInterval + "\n" +
					"Precision: " + precision + " (" + precisionStr + " seconds)\n" + 
					"Root delay: " + new DecimalFormat("0.00").format(rootDelay*1000) + " ms\n" +
					"Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion*1000) + " ms\n" + 
					"Reference identifier: " + referenceIdentifierToString(referenceIdentifier, stratum, version) + "\n" +
					"Reference timestamp: " + timestampToString(referenceTimestamp) + "\n" +
					"Originate timestamp: " + timestampToString(originateTimestamp) + "\n" +
					"Receive timestamp:   " + timestampToString(receiveTimestamp) + "\n" +
					"Transmit timestamp:  " + timestampToString(transmitTimestamp);
			}
			
			
			
			/**
			 * Converts an unsigned byte to a short.  By default, Java assumes that
			 * a byte is signed.
			 */
			public static short unsignedByteToShort(byte b)
			{
				if((b & 0x80)==0x80) return (short) (128 + (b & 0x7f));
				else return (short) b;
			}
			
			
			
			/**
			 * Will read 8 bytes of a message beginning at <code>pointer</code>
			 * and return it as a double, according to the NTP 64-bit timestamp
			 * format.
			 */
			public static double decodeTimestamp(byte[] array, int pointer)
			{
				double r = 0.0;
				
				for(int i=0; i<8; i++)
				{
					r += unsignedByteToShort(array[pointer+i]) * Math.pow(2, (3-i)*8);
				}
				
				return r;
			}
			
			
			
			/**
			 * Encodes a timestamp in the specified position in the message
			 */
			public static void encodeTimestamp(byte[] array, int pointer, double timestamp)
			{
				// Converts a double into a 64-bit fixed point
				for(int i=0; i<8; i++)
				{
					// 2^24, 2^16, 2^8, .. 2^-32
					double base = Math.pow(2, (3-i)*8);
					
					// Capture byte value
					array[pointer+i] = (byte) (timestamp / base);

					// Subtract captured value from remaining total
					timestamp = timestamp - (double) (unsignedByteToShort(array[pointer+i]) * base);
				}
				
				// From RFC 2030: It is advisable to fill the non-significant
				// low order bits of the timestamp with a random, unbiased
				// bitstring, both to avoid systematic roundoff errors and as
				// a means of loop detection and replay detection.
				array[7] = (byte) (Math.random()*255.0);
			}
			
			
			
			/**
			 * Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a
			 * formatted date/time string. 
			 */
			public static String timestampToString(double timestamp)
			{
				if(timestamp==0) return "0";
				
				// timestamp is relative to 1900, utc is used by Java and is relative
				// to 1970 
				double utc = timestamp - (2208988800.0);
				
				// milliseconds
				long ms = (long) (utc * 1000.0);
				
				// date/time
				String date = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss").format(new Date(ms));
				
				// fraction
				double fraction = timestamp - ((long) timestamp);
				String fractionSting = new DecimalFormat(".000000").format(fraction);
				
				return date + fractionSting;
			}
			
			
			
			/**
			 * Returns a string representation of a reference identifier according
			 * to the rules set out in RFC 2030.
			 */
			public static String referenceIdentifierToString(byte[] ref, short stratum, byte version)
			{
				// From the RFC 2030:
				// In the case of NTP Version 3 or Version 4 stratum-0 (unspecified)
				// or stratum-1 (primary) servers, this is a four-character ASCII
				// string, left justified and zero padded to 32 bits.
				if(stratum==0 || stratum==1)
				{
					return new String(ref);
				}
				
				// In NTP Version 3 secondary servers, this is the 32-bit IPv4
				// address of the reference source.
				else if(version==3)
				{
					return unsignedByteToShort(ref[0]) + "." +
						unsignedByteToShort(ref[1]) + "." +
						unsignedByteToShort(ref[2]) + "." +
						unsignedByteToShort(ref[3]);
				}
				
				// In NTP Version 4 secondary servers, this is the low order 32 bits
				// of the latest transmit timestamp of the reference source.
				else if(version==4)
				{
					return "" + ((unsignedByteToShort(ref[0]) / 256.0) + 
						(unsignedByteToShort(ref[1]) / 65536.0) +
						(unsignedByteToShort(ref[2]) / 16777216.0) +
						(unsignedByteToShort(ref[3]) / 4294967296.0));
				}
				
				return "";
			}
		}
}
